1.25Cr-0.5Mo | 1.25Cr-0.5Mo-Si

Chemical Composition & Characteristics

The 1.25Cr-0.5Mo (also known as “1-1/4Cr-1/2Mo”) steel is a typical low alloy heat-resistant steel of the Cr-Mo steel family. It is widely used for applications at elevated temperatures. The figures “1.25” and “0.5” denote the nominal chemical composition of chromium and molybdenum alloying elements respectively. The chromium provides improved oxidation and corrosion resistance, and, the molybdenum increases creep strength at elevated temperatures. In ASME Codes, the 1.25Cr-0.5Mo generally refers to castings. Various wrought 1.25Cr-0.5Mo steels are furnished with necessary addition (0.5~1.0%) of silicon element, thus, are designated as “1.25Cr-0.5Mo-Si“. The silicon increases the elevated-temperature strength of steel. It also increases the resistance to scaling of the low-chromium steels in air at elevated temperatures. The 1.25Cr-0.5Mo steel may be furnished in annealed, normalized and tempered, or quenched and tempered condition.

Product Forms, Standards & Grades

Product Forms	Standards & Grades
Castings	ASTM A217 WC6 ASME SA-217 WC6
Cast Pipes	ASTM A426 CP11 ASME SA-426 CP11
Bars	ASTM A739 B11 ASME SA-739 B11
Forgings	ASTM A182 F11 ASME SA-182 F11 ASTM A336 F11 ASME SA-336 F11
Seamless & Welded Fittings	ASTM A234 WP11 ASME SA-234 WP11
Seamless Tubes	ASTM A213 T11 ASME SA-213 T11
Welded Tubes	ASTM A250 T11 ASME SA-250 T11
Seamless Pipes	ASTM A335 P11 ASME SA-335 P11
Welded Pipes	ASTM A691 1.25Cr ASME SA-691 1.25Cr
Forged Pipes	ASTM A369 FP11 ASME SA-369 FP11
Plates	ASTM A387 11 ASME SA-387 11

The 1.25Cr-0.5Mo (1.25Cr-0.5Mo-Si) steels can be provided in a variety of product forms in accordance with corresponding ASTM/ ASME standard specifications.

Physical Properties

The density of 1.25Cr-0.5Mo steel is 7750 kg/m³, and the Poisson’s ratio is 0.30. The melting temperature range is 2600°F-2800°F. The typical values of thermal expansion (instantaneous, mean, and linear), thermal conductivity, thermal diffusivity, and modulus of elasiticity of the 1.25Cr-0.5Mo steel are listed in tables below. These values are listed as a function of temperature from 20°C to as high as 825°C.

Temp. °C	A	B	C
20	11.5	11.5	0
50	12.0	11.8	0.35
75	12.3	11.9	0.65
100	12.7	12.1	0.97
125	12.9	12.3	1.3
150	13.2	12.4	1.6
175	13.5	12.6	2.0
200	13.8	12.7	2.3
225	14.0	12.9	2.6
250	14.3	13.0	3.0
275	14.6	13.2	3.4
300	14.9	13.3	3.7
325	15.1	13.4	4.1
350	15.4	13.6	4.5
375	15.7	13.7	4.9
400	15.9	13.8	5.3
425	16.1	14.0	5.7
450	16.4	14.1	6.1
475	16.5	14.2	6.5
500	16.7	14.4	6.9
525	16.8	14.5	7.3
550	16.9	14.6	7.7
575	17.0	14.7	8.2
600	17.0	14.8	8.6
625	17.1	14.9	9.0
650	17.1	15.0	9.4
675	17.1	15.1	9.9
700	17.1	15.1	10.3
725	17.1	15.2	10.7
750	17.2	15.3	11.1
775	17.4	15.3	11.6
800	17.7	15.4	12.0
825	18.1	15.5	12.5

*Thermal expansion for 1.25Cr-0.5Mo steels: Coefficient A is the instantaneous coefficient of thermal expansion ×10⁻⁶(mm/mm/°C). Coefficient B is the mean coefficient of thermal expansion ×10⁻⁶(mm/mm/°C) in going from 20°C to indicated temperature. Coefficient C is the linear thermal expansion (mm/m) in going from 20°C to indicated temperature. All values are extracted from Material Group 1 of ASME BPVC Section II Part D Table TE-1

Temp. °C	TC	TD
20	41.0	11.87
50	40.8	11.47
75	40.7	11.16
100	40.6	10.88
125	40.5	10.60
150	40.4	10.33
175	40.3	10.08
200	40.1	9.82
225	39.8	9.57
250	39.5	9.32
275	39.1	9.07
300	38.7	8.82
325	38.3	8.57
350	37.8	8.32
375	37.3	8.06
400	36.8	7.81
425	36.3	7.55
450	35.8	7.29
475	35.3	7.03
500	34.8	6.77
525	34.4	6.50
550	33.9	6.24
575	33.4	5.97
600	32.8	5.69
625	32.2	5.42
650	31.6	5.14
675	30.7	4.78
700	29.1	4.37
725	27.6	3.83
750	26.7	2.69
775	-	1.26
800	-	5.06
825	-	7.74

*Nominal coefficients of thermal conductivity and thermal diffusivity for 1.25Cr-0.5Mo steels: TC is the thermal conductivity, W(m·°C), and TD is the thermal diffusivity, 10⁻⁶m²/sec. The specific heat [J/(kg·°C)] can be calculated by the equation: TD = TC / (Density × specific heat). All values are extracted from Material Group C of ASME BPVC Section II Part D Table TCD.

Temp.	E
-200	218
-125	213
-75	210
25	204
100	200
150	197
200	193
250	190
300	186
350	183
400	179
450	174
500	169
550	164
600	157
650	150
700	142

*Modulus of elasticity E (×10³ MPa) for given temperatures (°C) of 1.25Cr-0.5Mo (1.25Cr-0.5Mo-Si) steels. All values are extracted from Material Group C of ASME BPVC Section II Part D Table TM-1.

Creep Strength & Rupture Strength

Due to the improved creep strength, 1.25Cr-0.5Mo steels can be used at temperatures as high as 649°C [1200°F]. It has comparable stress-rupture and creep properties at elevated temperatures as that of 1.0Cr-0.5Mo alloy steels.

Air Hardening Characteristics

Temp. °F [°C]	Hardness, HB
Annealed	156
1400 [760]	149
1500 [815]	156
1600 [870]	179
1650 [900]	187
1750 [955]	229
1850 [1010]	223
1950 [1065]	212

Hardness is one of the key parameters of the heat-resistant steel. In order to determine the hardness values after air cooling, several pieces of round specimens (25 mm in diameter and 50 mm in length) were sliced longitudinally and heated. The hardness values are measured after air cooling from designated temperatures and presented in the table above.

Supply Chain

Due to the huge consumption in many elevated-temperature applications, a complete supply chain for the 1.25Cr-0.5Mo steel has formed in China’s steel industry. It means that this steel is 100% recyclable and full spectrum of starting materials are commercially available. Thus, we can not only supply 1.25Cr-0.5Mo steels in various product forms such as casting, forging, pipe, tube, fitting, valve part, and pressure vessel, but also reduce the cost to the minimum.